STEGANALYSIS

1. PERFORMANCE EVALUATION ON
DIFFERENT STEGNOGRAPHIC
ALGORITHMS
JAYESH S, AP , Archana College Of Engineering – ALAPPUZHA
AJAL.A.J , ASSISTANT PROFESSOR , FISAT – KOCHI
VINOTHKUMAR.S , Scholar at PRIST University, Thanjavur
HRIDYA K S - A P , K R G C E W – ALAPPUZHA

2. http://edition.cnn.com/video/?/video/world/2012/04/30/pkg-robertson-al-qaeda-documen

3. http://www.usatoday.com/tech/news/2001-02-05-binladen.htm

4. Contents
Steganography and Steganalysis
Steganographic schemes
System Features
Improvement / Comparison
Conclusion and Future Work

5. What is Steganography?
 Origin of the term: steganos: secret – graphy:
writing

6. Steganalysis
♦ Passive steganalysis
– detect the presence or absence of a message
♦ Active Steganalysis
– Estimate the message length and location
– Estimate the Secret Key in embedding
– Extract the message
crypto + graphy ( secret + writing )
stegano + graphy ( cover + writing )

7. Types of Steganalysis
 Targeted Steganalysis
 Relys on knowing the method used to hide the data & using
known distinguishing statistics to detect stego images
 Sometimes steganalysts reverse engineer steganographic
methods
 Blind Steganalysis
 Most beneficial to forensics because it’s not based on
knowing the algorithm
 Most difficult because the type of images and method of
hiding data are enormous and continuously changing.
 The current trend is to develop a neural network using
training images and multiple statistical features. A method
beyond the scope of this talk.

8. Other previous work
in steganalysis
 Provos analyzed two million eBay images (jpeg) but although he
identified thousands of “suspicious” images, nothing conclusive was
recovered from any of them
 A statistical method based on pairs of values (POVs) was
introduced by Pfitzmann and Westfeld, providing very reliable
results if the message was placed in sequential pixel locations in the
image
 Fridrich et al has a statistical method called RS steganalysis for
detection of LSB embedding
 It uses dual statistics derived from spatial correlations in an image
 In a typical cover image the LSB plane can (to some degree) be
predicted from the remaining 7 bit planes
 This intuitive idea is formulated mathematically resulting in the RS
method
 The safe-bit rate for the LSB embedding algorithms is less than

9. Modern Stego Techniques
Outguess
 Stego framework is created by embedding
hidden data using redundancy of cover image.
 Outguess preserves statistics of the BDCT
coefficients histogram
 Stego takes two measures before embedding
data
- Redundant BDCT coefficients, which has least
effect on cover image.
- Adjusts the untouched coefficients.
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10. Modern Stego Techniques (cont’d.)
F5
• Works on JPEG format only.
• Two main security actions against steganalysis
attacks:
- Straddling: scatters message uniformly over
the cover
image
- Matrix Embedding: Improves embedding
efficiency (no. of bits/ change of BDCT coeff.)
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11. Modern Stego Techniques (cont’d.)
MB (Model-based Steganography)
• Correlates embedded data with cover
image
• Splits cover image into two parts
- Models parameter of distribution of second given first
part
- Encodes second part using model and hidden message
- Combine these two parts to form stego image
• MB1 operates on JPEG images, uses Cauchy
distribution to model JPEG histogram
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12. Future of Steganography
 The most important use of
steganographic techniques will
probably lie in the field of digital
watermarking
 Might become limited under laws -
governments claimed that
criminals use steganography to
communicate
...the End